A woman was transported via medical helicopter to a Boston hospital after a bicycle accident caused her head injuries on Sunday.

A pack of bicyclists riding down North Street crashed when turning on to Smith Avenue on Sunday around 10:30 a.m., leaving one woman semi-conscious, Fire Chief Tim Bailey said. The woman, around 50 years old from Marlborough, was taken to Massachusetts General Hospital in a medical helicopter.

Bailey said a group of bicyclists were riding close together on North Street, and when the pack turned, one bike did not make the curve with the other riders causing the wheels to snare. The injured woman was flung from her bike, Bailey said, and sustained head injuries.

Paramedics called the helicopter because the woman was semi-conscious, Bailey said, though the injuries did not appear to be life threatening.